A conventional wet friction plate has an erratic pattern of irregularities on the surface that frictionally engages a mating plate. These irregularities sometimes cause abnormal noises and vibration upon engagement of a clutch or a brake incorporating the friction plate. The generation of noise and vibration is referred to as “initial shudder”.
The problem of controlling shudder is addressed in Unexamined Japanese Patent Publication No. 133158/1997. However, the approach described in the Japanese Patent Publication is to control the thickness of oil films between wet friction plates. This approach requires a complex structure to achieve and maintain an oil film having optimal thickness, and the complex structure, in turn results in a high manufacturing cost.
The present invention provides a wet friction plate which is capable of controlling initial shudder at low cost.